Failure case study of reinforced-concrete foundations of wind turbine towers

Wind loads on wind turbine towers (WTTs) and fan blades are transferred to the reinforced-concrete (RC) foundations by embedded steel anchor bolts or circular steel tubes (CSTs). Understandably, the stability and bearing capacity of the RC foundations are important to the safety of WTTs. The design principle and operation of RC WTT foundations are analysed and discussed in this paper. The load-carrying capacity of the RC foundations is studied based on the mechanical behaviour of embedded CSTs in concrete. The study shows that the concrete over the lower steel flange plate of the CST in RC foundations can be easily fractured and crushed under extreme typhoon loads. This mode of failure is frequently neglected in the design of RC foundations for WTTs. As a result, failure of WTTs occurs relatively easily when they are subjected to extreme typhoon loads. The failure case study also indicates that serious failures are associated with such a design defect. Based on the analysis and the case study, some recommendations are put forward in order to improve the design of RC foundations for WTTs.